1. Field of the Invention
The present invention relates to devices that enable the suspension of acoustic bases so as to make it possible to combat the effects of swells of the sea.
2. Description of the Prior Art
Acoustic bases, namely sets of acoustic transducers that enable the reception or transmission of acoustic signals in water, notably for sonars, are often fixed beneath the hull of a ship within a protective shell called a sonar dome, itself generally filled with an acoustically adapted protective liquid. Since the ships generally shift under the effect of the waves, the acoustic beam, both in transmission and in reception, follows the motions of the base, and it soon becomes necessary to compensate for these shifts. Although electronic compensation is possible, the generally preferred method, at least to compensate for the biggest motions, is to suspend the base in such a way that it tends to remain vertical despite these motions of the ship. To make the explanation easier to understand, and to simplify the terms, it may be said, in considering the relative motion and assuming that the ship is still, that the base swings angularly about its point of suspension from the hull. Although it is possible to think of making the dome too oscillate, the usual practice, for mechanical as well as for hydrodynamic reasons, is to fix the dome rigidly to the hull of the ship and to suspend the base inside this dome in which it oscillates with relative freedom. Furthermore, since the effects of the waves are far more pronounced in rolling than in pitching motions, the base is generally suspended so that it can oscillate laterally with respect to the axis of the ship: this compensates for the rolling motions. At the same time the base remains rigidly fixed with respect to the longitudinal axis: this makes it follow the pitching motions which are smaller than the rolling motions.
If a small base could be placed in a big dome, this base would have all the space needed to move within the dome without striking the dome walls. This approach is not generally adopted because the dome slows down the ship and therefore has to be made as small as possible in taking account of the dimensions of the base that it has to contain. Under these conditions, the base tends to strike the internal walls of the dome as soon as the rolling reaches a certain magnitude. These impacts are all the more dangerous as the base which, for example, has the shape of a circular drum with a vertical axis, has relatively sharp corners and considerable weight. Despite the shock absorption provided by the liquid filling the dome, there remains a risk, therefore, that the impacts will batter down the dome. To prevent collision of this kind, it then becomes necessary to use various corrective devices such as stops that restrict the pendular deflection of the base. These corrective devices are far from satisfactory since, precisely in limiting the motions of the base, they tend to fix it rigidly to the hull and therefore counter the compensation that is to be obtained by suspending it pendularly.